1. Field of the Invention
The present invention relates to a method and apparatus for fabricating a fibrous pad containing a layer of powder therein, and more particularly, to a method and apparatus for intermittently spraying particulate powder material onto predetermined locations of a moving fibrous substrate to form a layer of particulate powder material within a predetermined portion of the fibrous substrate.
2. Description of the Prior Art
Hygenic articles such as disposable diapers, sanitary napkins, incontinence pads and sick bed sheets must have a high absorption capacity to effectively retain eliminated body fluids for acceptable periods of time. Early hygenic articles of this type employed cellulose wadding, fluff cellulose or absorbent cotton as absorbent materials. The problem with these materials is that their absorbent capacity is relatively small compared to their volume. In order to improve the moisture retaining capacity of hygenic articles made from these materials, the volume of such absorbent materials in the hygenic article must be increased. This produces a bulky product which is unacceptable in many hygenic articles, particularly sanitary napkins.
To reduce the volume and size of hygenic articles, and increase their absorbent capacity, highly absorbent materials have been developed and are combined within a fluid absorbent fibrous substrate composed of cellulose fluff, wood pulp, textile fibers or other non-woven, woven, fibrous materials. Such highly absorbent materials which have a high capacity for absorbing water and body fluids are known in the art and generally consist of water insoluble, water-resisting organic polymers. These polymers are partially or wholly synthetic and are commercially available in fine grain, particulate form.
Various techniques have been developed to distribute and locate the highly absorbent material on or within the fibrous substrate. One prior art method of combining powder with a fibrous substrate comprises applying the powder to a top surface of the substrate. For example, U.S. Pat. No. 4,800,102 discloses a method and apparatus for spraying powder onto a fibrous substrate through a rotatable disc member having at least one opening through which powders continuously sprayed from a spraying means can reach the substrate. The apparatus also includes scraper means disposed above and closely adjacent to the disc member for deflecting powder from the surface of the disc member through an opening. A lower powder receiving member is disposed beneath the scraper means for collecting powder material deflected by the scraper means. An upper powder sucker is disposed above the disc member adjacent the scraper means and is effective to remove from the disc member any powder which is not forced by the scraper means through the opening. The powder material recovered by the lower powder member and the upper sucker are transported back to a powder supply. U.S. Pat. No. 4,861,405 also discloses a method and apparatus for spraying powder to a top surface of a laminated continuous sheet. The system of this patent utilizes the speed of the continuous sheet to create an air flow zone of a predetermined thickness over a predetermined surface of the continuous sheet. Powder is continuously fed to the air zone by free fall through a conduit and by utilizing a decreasing-pressure phenomenon produced by the air flow in which the pressure decreases as the predetermined surface of the laminated continuous sheet is approached. Powder is caused to adhere to the predetermined surface as it is drawn toward the predetermined surface of the laminated continuous sheet.
Another prior art method disclosed in U.S. Pat. No. 4,882,204 utilizes an aerosol spray nozzle of an aerosol container having absorbent powder particles to form a diaper having highly absorbent material over the entire length and width of the diaper. The spray force drives many of the powder particles into subsurface layers of the diaper.
U S Pat. No 4,675,209 discloses another prior art method for applying highly absorbent material onto a top surface of a moving substrate. This method includes the steps of dispensing a melt adhesive film on precisely defined areas of the substrate, covering such areas with the absorbent material and then removing excess material which did not adhere to the adhesive coated areas.
Another prior art method of combining moisture absorbent material with a fibrous substrate comprises intermixing highly moisture-absorbent material with fibrous material in a forming chamber. U.S. Pat. No. 4,927,346 discloses an apparatus for forming a non-woven pad consisting of fibrous material in which highly absorbent particles are intermixed with fibrous material throughout a predetermined portion of the thickness of the pad. The non-woven pad is formed on top of a conveyor moving through a chamber which has a duct connected to a vacuum source operable to draw fibrous material injected into the chamber onto the conveyor. A spray gun atop the conveyor discharges moisture absorbent material at a predetermined velocity, such that the moisture absorbent material is intermixed with the fibrous material throughout a center layer of the thickness of the non-woven pad while forming boundary layers on either side of the center layer which are substantially free of moisture absorbent material. The spray gun is operable intermittently to form spaced, sharply defined areas along the length and width of the non-woven pad wherein each area has moisture absorbent material interspersed throughout a portion of the thickness thereof.
The conventional devices described above have problems associated with loss of moisture absorbent material through the conveyor in the forming chamber. In addition, the prior art methods which produce a substrate having highly absorbent material throughout the entire length and/or width produces substantial waste because in subsequent forming operations the non-woven pad is cut to the desired length of the hygenic article. Prior art methods which produce a substrate having the absorbent material on a top surface have the disadvantage that the moisture absorbent capacity of the non-woven pad is substantially limited. This causes "gel blockage" wherein the moisture absorbent material at the top of the pad becomes saturated with fluid and prevents the transfer of moisture to the remaining portion of the pad. As a result, the fluid is retained at the surface of the pad in contact with the wearer of the hygenic article causing discomfort. Another disadvantage with these methods is that the moisture absorbent material is of a particulate or granular form and can be dislodged from the type of pads which are not sealed at the ends.
Product specifications for present hygenic articles require high absorbency material to be centrally located within a fibrous pad and it may not extend to the edges or ends of the pad. In addition, the absorbent material must be applied in a manner which does not damage or pass through the pad. Conventional devices and techniques, such as those discussed above, have not, however, been sufficiently capable of efficiently producing a fibrous pad having particulate powder material distributed in a predetermined portion of the thickness, and across the length and width, of the pad. In addition, the conventional forming techniques have not been sufficiently able to deliver powder materials in a substantially uniformly dispersed configuration that can be readily directed and distributed into predetermined locations and patterns within the fibrous pad.